Talk:Time dilation

About twin paradox

The article explanation about twin paradox is that the earth brother will only experience negligible acceleration, due to rotation and revolution of Earth. In twin paradox page something more intuitive is provided, that the turnover acceleration of the traveling twin makes the difference. I assume that the rotation and revolution of the earth, as explanation, is not only a special case but also it presupposes something useless. It presupposes that the traveling twin direction is perpendicular to the rotation axis or parallel to the plain of revolution. I am a biologist not a physicist, so someone more qualified can explain me.Vardos (talk) 20:47, 16 August 2018 (UTC)

Explanations about this can be on-topic at our wp:Reference desk/Science. Here we discuss the article, not its content. See wp:Talk page guidelines. Good luck. - DVdm (talk) 08:43, 17 August 2018 (UTC)

This criticism appears to be a misapplication of wikipedia rules. The question is directly relevant to the article, and the article is nothing but its content. To argue that users cannot discuss article content would seem to imply that article content can only be changed, and that no discussion about such content can ever take place. This is clearly not the intent of any reasonable set of participation rules. In fact, the Talk page guidelines explicitly say "Comment on content, not on the contributor."

Regarding the initial question, it seems directly relevant to the article, since the explanation currently provided implies, I assume incorrectly, that only differences in acceleration are important in the twin paradox. As the 2013-11-26 version of the article says:

The dilemma posed by the paradox, however, can be explained by the fact that the traveling twin must markedly accelerate in at least three phases of the trip (beginning, direction change, and end), while the other will only experience negligible acceleration, due to rotation and revolution of Earth. During the acceleration phases of the space travel, time dilation is not symmetric.

If only differential acceleration mattered, any acceleration (assuming one could deal with the likely fatality such acceleration would cause to any human twin) to some high % of C, turn-around, and deceleration to again match velocity with the "stationary" twin should be sufficient to induce the same time dilation of a longer term journey. Yet it is my understanding that the length of time the traveling twin actually travels at near C is the primary determining factor in observable time dilation. Assuming that no far weirder effects of relativistic travel than I have read/heard are operating (such that, for example, a 100 year journey at .99999999 C creates the same time dilation as a 1 year journey at .99999999 C), the example given is at the very least incomplete. The earlier observation by Vardos seems directly relevant to the article. LUxlii (talk) 01:58, 27 November 2018 (UTC)

The acceleration explanation is not true, according to FermiLab's Don Lincolm: https://www.youtube.com/watch?v=GgvajuvSpF4 LosD (talk) 09:14, 16 January 2019 (UTC)

Edge of the universe

Paragraph 2 of Time dilation#Velocity time dilation says “At a constant 1 g traveling up to 0.99999999 c it would take 30 years to reach the edge of the universe 13.5 billions lightyears away. [13]” But I thought that there’s a symmetry feature of the universe such that no place is the “edge” of the universe. Should this be reworded? Loraof (talk) 22:54, 12 November 2018 (UTC)

They probably meant the edge of the the entire known Universe, as it is expressed in the previous—better worded and sourced—sentence. I have removed the repeated poorly youtube-sourced sentence. - DVdm (talk) 07:32, 13 November 2018 (UTC)

I also removed the remainder of that sentence, per less relevant and unsourced. - DVdm (talk) 07:36, 13 November 2018 (UTC)

Velocity time dilation

The statement in the Velocity time dilation section of Sergei Krikalev that "He gained 22.68 milliseconds of lifetime" seems incorrect. Krikalev gained no lifetime from his own perspective, but his idiosyncratic reference frame slowed such that his clock is that much behind a stationary clock. Perhaps it should be reworded to something like "He is 22.68 milliseconds younger than he would have been had he stayed stationary on Earth." Alas, I am far from sufficiently versed in relativistic time effects to be comfortable making such a change without some discussion attempt first. LUxlii (talk) 02:08, 27 November 2018 (UTC)

 Done: see [1]. Good suggestion! - DVdm (talk) 06:33, 27 November 2018 (UTC)

Some suggestions ... again.

As I expected you made no use of the suggestions I presented on 2nd November 2017. I hope to be more lucky this time ! I think you are fully aware that good quality clocks , and at least atomic clocks , are not sensitive to displacement. And if the clocks are moving at constant speed , that is predicted by the very first postulate of special relativity !

Unfortunately Einstein and his followers never used vectors , and so never spoke of units of time. That was a consequence of the railway examples then currently used. Later on they switched to tensor calculations , again without vectors. So if I try to find direct sources, I find none ! Nobody tells us that the clock of the train controller has the same rhythm than the clock of the station master !

But that is true !!

Please take a look at following statements :

I/ Between two time unit vectors we have :

$1/\qquad e_{0}\cdot f_{0}=\gamma =\cosh {\alpha }$

where $\alpha$ is the hyperbolic "angle" between $e_{0}$ and $f_{0}$ . In geometric algebra we write :

$2/\qquad f_{0}=exp^{i\alpha }e_{0}=(\cosh {\alpha }+i\sinh {\alpha })e_{0}=\cosh {\alpha }e_{0}+\sinh {\alpha }e_{1}$

$3/\qquad i=e_{1}e_{0}=f_{1}f_{0}=e_{1}\wedge e_{0}=f_{1}\wedge f_{0}$

It is crystal clear that (1) explains completely traditional velocity time dilations and reciprocity !

II/ Taylor and Wheeler introduce wristwatch time for curved time paths. Thus they admitted silently that their watches were not sensitive to displacement !

III/ Finally abstract space time could not exist if there were no units of time and of space !

Thus we may conclude that in the present article there are too much hidden truths. Introduction of chrono-geometry could perhaps be a possible smooth solution ? Cordially. --Chessfan (talk) 18:56, 2 March 2019 (UTC)

Gravitational time dilation

The article repeatedly uses wording that suggests that dilation is related to the strength of the gravitational field. This is somewhat misleading. It should be relatively simple to improve this, as the relevant parameter is the local depth of the gravitational potential well. PhysicistQuery (talk) 00:14, 19 July 2019 (UTC)

But according to the literature, time dilation is related to the strength of the gravitational field. - DVdm (talk) 10:01, 19 July 2019 (UTC)

I'll look at this when I have a chance. Depth within the gravitational potential well is correct. If the article says that strength of the gravitational field is the relevant parameter, the article is wrong, or at least, worded in a misleading fashion. Prokaryotic Caspase Homolog (talk) 10:34, 21 July 2019 (UTC)

Yuck. I had never looked at the article as a whole before; my only previous contribution had had been to add the figure File:Time_Dilation_vs_Orbital_Height.png to replace Time.dilation.to.orbital.height.svg, which was completely messed up and which I requested to be deleted. This article needs a major revamp, but lots of it will have to be done by somebody other than me. I'm OK with the SR parts, but I would not consider myself any sort of expert in GR. Prokaryotic Caspase Homolog (talk) 10:47, 21 July 2019 (UTC)

Corrected the egregious errors, but the article as a whole is too much a mishmash for me to tackle. There are more important articles to work on, for instance Special relativity, whose section on dynamics is completely inadequate. Prokaryotic Caspase Homolog (talk) 06:22, 22 July 2019 (UTC)

Good action, this. IMO it just needed a little change - DVdm (talk) 06:28, 22 July 2019 (UTC)

Thanks! Prokaryotic Caspase Homolog (talk) 06:40, 22 July 2019 (UTC)

Does time dilation give you extra time?

Does time dilation give you extra time, so that you can get more done? 2A00:23C5:C105:7B00:A8B8:F512:2799:B80D (talk) 18:53, 11 August 2019 (UTC)

Here we can only discuss the article, not its subject—see wp:Talk page guidelines. You can try asking at the wp:Reference desk/Science. - DVdm (talk) 11:45, 12 August 2019 (UTC)

Summary

Time dilation is a Galilean transformation calculation, of simple geometry, with the speed of light c being calculated as constant, between two visual light observers of which one is moving and yields the same time for both observers (used correctly). The same equation provides correction for an observer who, by visual perception, has mis-measured time by assuming c2==c1+v, which it does not. Which observer moves matters for doppler, but not for dilation. c is limited to remaining c in space thus there is no second inertial frame it can be in. The observers must observe v by the simple Galilean transform. If light is not used in measurement the equation is completely invalid. — Preceding unsigned comment added by 2601:143:400:547B:94F6:2347:9F50:AC34 (talk) 00:23, 28 August 2019 (UTC)